An information processing system and method using an encryption key block sets sub-trees classified based on data processing ability of the devices (capability) in a key tree in which respective keys are corresponded to a root, nodes and leaves of a tree in which a plurality of devices are constituted as the leaves, generates a sub-enabling key block which is effective for an entity in a managing subject of each sub-tree (entity), and generates an enabling key block decodable only by the entities having common capability. Also, an information processing system and method using an encryption key block manages a partial tree of a key tree (sub-tree), generates a sub-enabling key block based only on a key set corresponding to nodes or leaves included in the sub-tree, and generates an enabling key block decodable only by selected entities by using the sub-enabling key block. Thus, it is possible to generate and distribute an enabling key block corresponding to data processing ability of a device and to manage devices by dividing a hierarchical key tree structure.